Field of the Invention
The present invention relates to an image formation optical scanner to be used for exposure in an image forming apparatus, an image forming apparatus equipped with the image formation optical scanner, and a non-transitory computer-readable recording medium storing an image forming apparatus optical scanning program.
Description of the Related Art
In an electrophotographic image forming apparatus such as a laser printer, a digital copier, or a normal paper facsimile machine, a laser beam modulated with an image signal is reflected at a rotating polygon reflecting mirror (polygon mirror), whereby the electrified surface of a photoreceptor is scanned with the laser beam. Thereby, an electrostatic latent image is formed on the electrified surface.
As such an image forming apparatus, there is proposed a device in which a light receiving sensor (=SOS (Start of Scan) sensor) is provided at a predetermined position before the position of starting laser scanning of a photoreceptor, and a forcibly emitted laser beam is detected by the SOS sensor. Based on the detected signal, output start timing of an image signal on each scanning line is controlled, and the rotational speed of the polygon mirror is controlled.
Japanese Patent Laid-Open No. 2004-126228 describes an apparatus having a plurality of laser light sources. When a polygon motor is actuated, the apparatus turns on an A-laser, and after detecting a BD signal based on the A-laser, turns off the A-laser and turns on a B-laser, and after detecting a BD signal based on the B-laser, turns off the B-laser and then forcibly turns on the A-laser again. This means that the A-laser and the B-laser are alternately turned on each time a BD signal is detected. Thereby, the lives of the laser light sources are allowed to be almost the same.
Further, Japanese Patent Laid-Open No. 2001-212999 describes that in the case of changing a resolution, resolution conversion is performed by thinning out surfaces of a rotating polygon mirror, without changing the rotational speed of the rotating polygon mirror. If resolution change is performed by changing the process speed, it takes time until the speed is stabilized, so that it takes time until printing. Further, as light emitting elements are lighted on the entire surfaces of the rotating polygon mirror, the lives of the light emitting elements are shortened. According to the above configuration, as there is no need to obtain a main scanning synchronous signal for the surface to be thinned out, it is possible to elongate the lives of the light emitting elements.
Further, in a polygon motor which is rotationally controlled by an SOS signal, it is needed to emit a laser in order to obtain an SOS signal, not only during printing performed by the image forming apparatus but also during standby.
Japanese Patent Laid-Open No. 2009-297917 describes that in a first mode which requires rotational accuracy of a polygon motor, rotation control is performed by BD control, while in a second mode which does not require rotational accuracy of the polygon motor, rotation control of the polygon motor is performed by FG control. The first mode includes a mode of forming a print image, a mode of forming a patch image, a mode of measuring a SOS cycle, and the like, and the second mode includes a mode at the time of flying start and the like.
As described above, if LD emission is required even during a long standby time, the life of a laser emission source becomes a problem to be solved. In particular, a standby time is very long, compared with the time taken for drawing for the number of durable sheets of an image forming apparatus, and laser emission during that time largely affects the life of the laser emission source.
However, in Japanese Patent Laid-Open No. 2004-126228 and Japanese Patent Laid-Open No. 2001-212999, no consideration is given to mitigation of a load affecting the life of a laser source during standby.
Further in Japanese Patent Laid-Open No. 2009-297917, while a mode is switchable depending on a difference in rotational accuracy, in FG control which is a second mode not requiring rotational accuracy, rotational accuracy deteriorates due to variations in magnetization, and further, the noise becomes large by rotation during standby. In particular, as driving of other functions in the image forming apparatus is stopped during standby, there is a problem that the driving noise of the rotating polygon mirror becomes remarkable and offends the ear. On the other hand, if normal SOS control having less noise during standby is performed, as described above, a problem regarding the life of the laser emission source is caused.
The present invention has been made with the above-described situation as a background. An object of the present invention is to provide an image formation optical scanner, an image forming apparatus, and a non-transitory computer-readable recording medium storing an image forming apparatus optical scanning program, enabling the life of a laser light source to be elongated during standby without causing a problem of loud noise.